A new study shows that mercury levels in the upper oceans are three times higher than they were in the Industrial Revolution times, raising concerns about the amount of mercury in our fish and on our plates.
A team of scientists from the United States, France and the Netherlands conducted a study aimed at calculating how much mercury in the world’s oceans are the result of human activities.
They found that the oceans contain about 60,000 to 80,000 tonnes of mercury pollution. Ocean waters shallower than about 100 meters have tripled in mercury concentration since the Industrial Revolution, while mercury in the oceans as a whole has increased roughly 10 per cent over pre-industrial times.
To reach these figures, the team turned to ocean levels of phosphate, a substance that is better studied in the oceans than mercury and that behaves in much the same way as mercury. Phosphate is a nutrient that, like mercury, is taken up into the marine food web by binding with organic material. Unlike mercury, however, it is not also a by-product of such human activities as burning coal and making cement.
By determining the ratio of phosphate-to-mercury in water deeper than 1,000 metres that has not been in contact with Earth’s atmosphere since the Industrial Revolution, the researchers were able to estimate mercury in the oceans that originated from natural sources such as the breakdown, or weathering, of rocks on land.
To calculate the contribution of mercury from human, the scientists needed a tracer–a substance that could be linked with major human activities that release mercury into the environment. They found it in one of the most well-studied and well-documented gases of the past 40 years: carbon dioxide. Because much of the mercury and carbon dioxide from human sources comes from the same activities, the team was able to derive with an index relating the two.
As alarming as their findings are, their predictions for the future are even more so. “The next 50 years could very well add the same amount we’ve seen in the past 150,” says lead scientists Carl Lamborg from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts.